Page 160
Demolished Waste as Coarse Aggregates
V.Sai Kiran Kumar
Scholar
BVSR Engineering College,
Chimakurthy.
B.Ravi Kumar
Scholar
BVSR Engineering College,
Chimakurthy.
K.Rami Reddy
Scholar
BVSR Engineering College,
Chimakurthy.
V.Subhashini
Scholar
BVSR Engineering College,
Chimakurthy.
Sk.Ayesha
Scholar
BVSR Engineering College,
Chimakurthy.
Pragada Rambabu
Assistant professor
BVSR Engineering College,
Chimakurthy.
ABSTRACT:
There is a large amount of demolished waste
generated every year in India and other developing
countries. Since very small amount of this waste is
recycled or reused. So, disposing this waste is a very
serious problem because it requires a large amount
of space. This study is a part of comprehensive
program wherein experimental investigations have
been carried out to evaluate the effect of partial
replacement of coarse aggregate by demolished waste
on compressive strength and workability of DAC
(Demolished Aggregate Concrete). For the study 3, 7
and 28 days compressive strengths were recorded.
The previous study on this project shows that the
compressive strength of the DAC (Demolished
Aggregate Concrete) is somehow resembles with the
conventional concrete if used in a proper amount up
to 80%. So in this study we have taken the
demolished concrete aggregate 10%, 20%, 40%, 60%,
80% by weight of the conventional coarse aggregate
and the concrete cubes were casted by that
demolished concrete aggregate then further tests
conducted such as workability , compressive strength
for that DAC and the result obtained are found to be
comparable with the conventional concrete.
INTRODUCTION
Concrete is basically made of aggregates glued by a
cement materials paste, which is made of cement
materials and water. Each one of these concrete
primary constituents, to a different extent, has an
environmental impact and gives rise to different
sustainability issues [Mehta 2001, 2002]. The current
concrete construction practice is thought unsustainable
because, not only it is consuming enormous quantities
of stone, sand, and drinking water, but also two billion
tons a year of Portland cement, which is not an
environment friendly material from the standpoint of
energy consumption and release of green-house gases
(GHG) leading to global warming. Furthermore, the
resource productivity of Portland-cement concrete
products is much lower than expected because they
crack readily and deteriorate fast. Since global
warming has emerged as the most serious
environmental issue of our time and since
sustainability is becoming an important issue of
economic and political debates, the next developments
to watch in the concrete industry will not be the new
types of concrete, manufactured with expensive
materials and special methods, but low cost and highly
durable concrete mixtures containing largest possible
amounts of industrial and urban byproducts that are
suitable for partial replacement of Portland cement,
Recycle aggregate concrete
Recycled-aggregate concrete (RAC) for structural use
can be prepared by completely substituting natural
aggregate, in order to achieve the same strength class
as the reference concrete, manufactured by using only
natural aggregates [Corinaldesi et al. 1999]. This is
obviously a provocation, since a large stream of
recycled aggregates to allow for full substitution of
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natural aggregates is not available. However, it is
useful to prove that to manufacture structural concrete
by partly substituting natural with recycled aggregates
by up to fifty percent is indeed feasible. In any case, if
the adoption of a very low water to cement ratio
implies unsustainably high amounts of cement in the
concrete mixture, recycled-aggregate concrete may
also be manufactured by using a water-reducing
admixture in order to lower both water and cement
dosage, or even by adding fly ash as a partial fine
aggregate replacement and by using a super plasticizer
to achieve the required workability [Corinaldesi &
Moriconi 2001].
Durability
Aspects related to the durability of recycled aggregate
concretes have already been studied. In particular,
attention has been focused on the influence of concrete
porosity on drying shrinkage and corrosion of
embedded steel bars as well as on concrete
carbonation, chloride ion penetration, and concrete
resistance to freezing and thawing cycles [Corinaldesi
& Moriconi 2002, Tittarelli & Moriconi 2002,
Corinaldesi et al. 2001, 2002b, Moriconi 2003].
Results showed that, when fly ash is added to
recycled-aggregate concrete:
1. the pore structure is improved, and particularly the
macrospore volume is reduced causing benefits in
terms of mechanical performance, such as
compressive, tensile and bond strength [Corinaldesi &
Moriconi 2002, Marconi 2003]. With respect to
ordinary concrete prepared with natural aggregate, the
only difference is a somewhat reduced stiffness of
recycled aggregate concrete containing fly ash, which
should be taken into account during structural design
[Moriconi 2003];
2. the drying shrinkage of recycled-aggregate concrete,
from a serviceability point of view, does not appear to
be a problem since, due to the reduced stiffness of this
concrete, the same risk of crack formation results as
for ordinary concrete under restrained conditions
[Moriconi 2003];
3. testing of concrete resistance against freezing and
thawing cycles showed no difference between natural-
aggregate concrete and high volume fly ash recycled-
aggregate concretes [Corinaldesi & Moriconi 2002];
4. the addition of fly ash is very effective in reducing
carbonation and chloride ion penetration depths in
concrete because of pore refinement of the cement
matrix due to a filler effect and pozzolanic activity of
fly ash. Moreover, the strong beneficial effect of the
presence of fly ash on chloride penetration depth is
quite evident since the chloride ion diffusion
coefficient in high volume fly ash concrete is one order
of magnitude less than that into concrete without a fly
ash addition [Corinaldesi & Moriconi 2002,
Corinaldesi et al. 2002];
LITERATURE REVIEW
Due to rapid development of industries and urban
areas waste generation is also increases, which is
unfavorably carrying out the environment. At present,
in India 27.8% of the total population living in cities,
which is 13.8% more than the year of 1947. There is a
shortage of about 55,000 million m 3 due to the
construction of new infrastructure which shows that
the demand of the aggregates in future increases. 750
million m 3 additional aggregate is required to fulfill
the demand of the road sector. There is a huge gap
between the demand and the supply of the aggregates
because giant amount of aggregates is required in the
housing and transportation nowadays. During
construction waste generated is about 40 kg per m 2 to
60 kg per m 2 . Similarly, during renovation, repair
and maintenance work 40 kg/m 2 to 50 kg/m 2 waste is
generated. The waste generated due to demolition of
the building is highest among all the wastes. If we
demolish permanent building about 300kg/m 2 waste
is generated and in case of demolition of semi-
permanent building 500kg/m2 waste is generated.
Environment must be protected for the survival of the
human beings and other lives on earth.
So environment consciousness, sustainable
development and preservation of natural resources
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should be kept in mind during the construction work
and industrialization. At present, demolished material
are dumped on land or treated as waste, which means
they cannot be utilized for any purpose. If we put the
demolished waste on land then the fertility of the soil
get decreases. 23.75 million tons of waste is generated
annually in India in the year of 2007 according to
Hindu Online. According to CPCB (Central Pollution
Control Board) Delhi, 14.5 million tons out of 48
millionwaste is generated from the construction waste
from which only 3% is utilized in the construction of
the embankment. In 100 parts of the construction
waste 40 parts are of concrete, 30parts of ceramics, 5
parts of plastics, 10parts of wood, 5 parts of metal and
10 parts of some other mixed compounds. There is a
huge demand of construction aggregate which is more
than 26.8 billion in all over the world. There is a quiet
increment in the utilization and demand of the natural
aggregates in India due to housing, road, construction
and infrastructure development.
During the time of Second World War the use of
demolished concrete waste was started, it was utilized
in the construction of the pavements. According to
Union Environment Ministry 12 million tons of the
construction and demolition waste is generated in the
year of 2013 but the current method adopted for the
management of this waste are landfill mainly which
causes a giant amount of the construction and
demolished waste deposition and such huge amount
affects the environment adversely. In India concrete,
bricks, sand, mortar and tile residues are the main
materials found in the demolished waste of buildings.
This waste can be recycled or process in to the
recycled demolished aggregates which can be utilized
in the concrete mixes. Demolished concrete aggregate
(DCA) is generally produced by the crushing of
concrete rubble, then screening and removal of
contaminants such as plaster, paper, reinforcements,
wood, plastics. Concrete made with this type of
recycled demolished concrete aggregate is called
Demolished aggregate concrete (DAC).
The main purpose of SSRG International Journal of
Civil Engineering (SSRG-IJCE) – volume 3 Issue 5 –
May 2016 ISSN: 2348 – 8352
www.internationaljournalssrg.org Page 118 this work
is to determine the basic properties of DAC made of
coarse recycled demolished concrete aggregate then to
compare them with the properties of concrete made
with natural aggregates concrete. Fine recycled
aggregate cannot be applied in the concrete which is
used for structures so we can ignore its amount 70-
75% aggregates are required for the production of
concrete. Out of this 60-67% is of coarse aggregate &
33-40% is of fine aggregate. India is in the top 10
users of the concrete due to rapid growth of
infrastructure. For the production of 1 ton of natural
aggregate 0.0046 million ton of carbon is emitted
which is harmful for the environment. So generation of
the carbon is also getting reduced if we use demolished
aggregates.
As the demolished aggregate is lighter than the natural
aggregate so the concrete made from such aggregate
possesses low density but the water absorption of the
demolished aggregate is higher than the natural
aggregate and the strength of the demolished
aggregates is somehow lesser than the natural
aggregates. So concrete made from these demolished
aggregate can be utilized where more strength is not
required e.g. in low rising buildings, in reinforced
concrete pavements etc.
EXPERIMENTAL INVESTIGATIONS
In this investigation an attempt has been made to study
the effect of demolished concretion physical properties
of concrete as replacement of coarse aggregate. The
property of concrete used, the procedure used for
mixing and tests conducted are represented in this
module.
The mixing has been done in the laboratory. The
properties considered in this study are strength and
workability. The experimental program is broadly
divided into following categories, viz.
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Workability characteristics
a)Slump
b)Compaction factor test
Strength characteristics
a)Compression test
MATERIALS USED
CEMENT
Cement can be defined as the bonding material having
cohesive & adhesive properties which makes it capable
to unite the different construction materials and form
the compacted assembly.
Ordinary Portland Cement (O.P.C)
It is hydraulic cement. It is used in the making of
concrete with property of setting and hardening, of
which when the chemical properties react with water,
O.P.C does not disintegrate in water as it sets and
hardens in water.
Ideal applications
1. Gives more flexibility to architects and engineers to
design sleeker and economical sections
2. On being mixed with other aggregates, O.P.C begins
to serve a dual purpose. One, it provides for the
concrete products to be workable when wet and two, it
provides them to be durable when dry.
3. It is extensively used by retaining walls and the
precast concrete block walls as a major component to
build a strong foundation of concrete.
4. Almost negligible chloride content results in
restraining corrosion of concrete structure in the
hostile environment
5. Produces highly durable and sound concrete due to
very low percentage of alkalis, chlorides, magnesia
and free lime in its composition.
6. It is also brought into usage in mortars, plasters,
screeds and grouts as a material which can be squeezed
into gaps to consolidate the structures.
Advantages
Roadways, runways, flyovers and bridges
For heavy defense structures like Bunkers
Pre-stressed concrete structures
Residential and commercial buildings
Pre-casted cubes
TESTS ON CEMENT
(a) Field Test
It is sufficient to subject the cement to field tests when
it is used for minor works. The following are the field
tests.
1. Have a good look at the cement. The lumps must not
be present. The color of cement should be greenish
grey.
2. Drill your hand into the cement bag, you should feel
cool.
3. Take a pinch of cement in between your fingers, it
should give you smooth and gritty feeling.
4. Take a handful of cement and throw it in a bucket
full of water, the particles should float for some time
before they sink.
(b) Laboratory Testing
Fineness test
Setting time test
Strength test
Soundness test
Heat of hydration test
Chemical composition test
The following tests were conducted to determine the
properties of cement.
SETTING TIME TESTS
(A) NORMAL CONSISTENCY
The objective of conducting the test is to find out the
amount of water to be added to the cement to get a
paste of normal consistency i.e.…, the paste of certain
solidity which is used to fix the quantity of water to be
mixed to the cement for the test for tensile strength,
compression strength, setting time and soundness of
cement as standard for comparing various cements as
it is the water cement ratio that decides the
characteristics of cement water paste.
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Standard consistency test of cement paste is defined as
the amount of water expressed as the percentage by
weight of cement which will permit the vicat plunger
to penetrate to a depth of 5mm to 7mm from the
bottom of vicat mould.
Plunger is the needle used for determining the normal
consistency of cement
Apparatus
Vicat apparatus with plunger & needles
Stop watch
Test Procedure
The test will be generally conducted at a
temperature of 27+20°C
Prepare a paste of weighed quantity of cement
(300gms) with weighed quantity of potable or
distilled water, taking care that the time of
gauging is not less than 3 minutes or more
than 5minutes and the gauging is completed
before any sign of setting occurs.
The gauging is counted from the time of
adding water to the dry cement until
commencing to fill the mould.
Fill the vicat mould with this paste resting
upon a non-porous plate.
Smoothen the surface of the paste, making it
level with the top of the mould.
Slightly shake the mould to expel the air.
In filling the mould operator‟s hands and the
blade of the gauging trowel shall only be used.
Immediately place the test block with the non-
porous resting plate, under the rod bearing the
plunger.
Lower the plunger gently to touch the surface
of the test block and quickly release, allowing
it sink into the paste.
Record the depth of penetration
Prepare trial pastes with varying percentages
of water and test as described above until the
plunger is 5mm to 7mm from the bottom of
the vicat mould.
(B) INITIAL SETTING
Initial setting time regarded as the time elapsed
between the movements that the water is added to the
cement, to the time that the paste starts losing its
plasticity. Initial needle is used for determining initial
setting time.
(C) FINAL SETTING TIME
Once the concrete is placed in the final position,
compacted and finished, it should lose its plasticity in
the earliest possible time so that it is least vulnerable to
damages from external destructive agencies. This time
should not be more than 10 hours which is often
referred to as final setting time. Final needle is used
for determining final setting time.
Fig 3.1 VICAT APPARATUS
Table: 3.1 Shows The Properties of Cement
AGGREGATES
Construction aggregate, or simply "aggregate", is a
broad category of coarse particulate material used in
construction, including sand, gravel, crushed d stone,
slag, recycled concrete and geo-synthetic aggregates.
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Aggregates are the most mined materials in the world.
Aggregates are a component of composite materials
such as concrete and asphalt concrete; the aggregate
serves as reinforcement to add strength to the overall
composite material.
Fine Aggregate
The aggregate which passes through 4.75mm IS Sieve
are termed as Fine Aggregate. They play a role of
filling the voids in the concrete mix. For increased
workability and for economy as reflected by use of less
cement, the fine aggregate should have a rounded
shape.
Coarse Aggregate
Coarse aggregate is a material that will pass the 80mm
sieve and will be retained on the 4.75mm sieve. As
with fine aggregate, for increased workability and
economy as reflected by the use of less cement, the
coarse aggregate should have a rounded shape. Larger
pieces offer less surface area of the particles than an
equivalent volume of small pieces. Use of the largest
permissible maximum size of coarse aggregate permits
a reduction in cement and water requirements.
WATER
Water is one of the most important elements in
construction but people still ignore quality aspect of
the element. The water is required for preparation of
motor, mixing of cement and concrete and for curing
work etc... During construction the quality and
quantity of water has much effect on the strength of
mortar and cement concrete in construction work. The
required quantity of water is used to prepare mortar or
concrete, but in practice it is seen that more water is
mixed to make the mix workable. This is a bad
practice and additional water weakens the strength of
cement paste. Extra water also weakens adhesive
quality.
Quality of Water
The water used for mixing and curing should be clean
and free from injurious quantities of alkalis, acid, oils,
salt, sugar, organic materials, vegetable growth and
other substances that may be deleterious to bricks,
stone, concrete or steel. Potable water is generally
considered satisfactory for mixing. The pH value of
water should be not less than 6. A popular yard sticks
to the suitability of water for mixing concrete is that, if
water is fit for drinking it is fit for making concrete.
This does not appear to be a true statement for all
conditions. Mixing and curing with sea water shall not
be permitted.
(a). To neutralize 200 ml sample of water. Using
phenolphthalein as an indicator, it should not require
more than 2 ml of 0.1 normal NAOH.
(b) To neutralize 200 ml sample of water, using methyl
orange as an indicator, it should not require more than
10 ml of 0.1 normal HCL
SAND
Sand is an inorganic material. It consists of small
angular or rounded or sharp grains of Silica. Sand is
formed by decomposition of sand stone under the
effect of weathering agencies. Various sizes or grades
of sand are formed depending on the amount of
wearing.
Characteristics of Good Sand
Should consist of coarse, angular, sharp and
hard grains.
Should not contain any organic matter.
Should be chemically inert.
Must be strong and durable.
Size of grains should be such that, next line
they pass through 4.75 mm I.S. sieve and are
entirely retained on 75µ I.S sieve.
The following tests were conducted to determine the
properties of sand
Natural Sand
This sand contains impurities like silt, silica
etc.
Natural Sand is made from different type of
stones so; binding strength varies.
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Natural Sand which is available today, don't
have fines below 600 microns in proper
gradation. So, voids in the concrete are not
filled properly & also increases cement
consumption.
Natural and gives low compressive strength as
compare to Artificial Sand.
As the voids are not filled properly, strength of
the concrete is not achieved.
As every truck of Natural Sand has different
fineness modules, every time concrete mix
design have to be changed.
Natural Sand is available in less quantity so; it
is costlier.
Because of sand dragging, riverbeds had
become deep. It is harmful to thenature.
Natural Sand contains pieces of bones, woods
etc. So it is not suitable as per Vastushastra.
TESTS CONDUCTED ON SAND
SIEVE ANALYSIS
The portion of sand retained on 4.75mm sieve for the
analysis. The quantity of sample to be taken shell
depends upon the maximum particle size contained in
the sand.
Separate the sample into various fractions by sieving
through the 4.75mm, 2.36 mm, 1.18mm, 600µm,
300µm, 150µm and pan. While sieving through each
sieve agitate the sieve so that the sample rolls in
irregular motion over the sieve. Any particle may be
tested to see if they will fall through but they shall not
be pushed through. If the soil appears to contain over
5% moisture, determine the water content of the
material.
When the soil sample contains less than 5% of
moisture it is not necessary to determine the moisture
content for dry weight computation and make all
determinations on the basis of wet weight only. If the
soil contains more than 20% of gravel particles and the
fines are very cohesive with considerable amounts
adhering to the gravel after separately wash the gravel
on 4.75mm sieve using sodium hexametaphosphate if
necessary.
Fig 3.2 Sieve shaker
Table 3.2 Sieve Analysis For Fine Aggregate
BULKING OF SAND
The absorbed moisture content in the fine aggregate
results in the bulking of volume. Moisture forms a thin
film around each particle and is known as adsorbed
moisture. This film of moisture exerts surface tension
which keeps the neighboring particles away from it.
This causes the bulking of the volume. The bulking
will depend upon the percentage of moisture content
up to certain limit and beyond that the further increases
in the moisture content results in the decrease in the
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volume. When the film of water around the particles
becomes thicker, the particle cannot hold it and it
becomes absorbed water and force of repulsion
between the particles decreases and finally becomes
zero. It can be noted that fine sand bulks more and
coarse sand bulks less.
Due to the bulking, fine aggregate shows completely
unrealistic volume. Therefore it is absolutely necessary
that consideration must be given to the effect of
bulking in proportioning the concrete by volume
Apparatus
Cylindrical beaker
Tray
Test Procedure
Take 300 ml sand say v1 and put it in a
container.
Empty the container on to a clean metal tray
without any loss of sand.
Add 1% of water by weight of sand and mix it
thoroughly by hand.
Put back the loose sand into the container
without tamping it.
Smooth and level the top surface of moist sand
and its depth v2.
Repeat the above procedure with
2%,3%......5%.
Fig 3.3 BULKING OF SAND APPARATUS
SPECIFIC GRAVITY AND WATER
ABSORPTION
Specific gravity of aggregate is defined as the ratio of
weight of aggregate to the weight of an equivalent
volume of water 270C water absorption is the weight
of the water absorbed in terms of oven dried weight of
aggregate.
The specific gravity of an aggregate is considered to be
a measure of strength or quality of the material having
low specific gravity are having generally weaker then
the those with higher specific gravity values.
Water absorption of aggregates gives strength of rock,
stone having more absorption are generally unsuitable
unless they are found to be acceptable based on
strength and hardness test.
Apparatus:
Pycnometer
Weighing machine
Test Procedure
Take 500 g of fine aggregate (the quantity
shall be in such a way that it should fill the
pycnometer up to two thirds of its volume) and
cleaned it thoroughly by washing it -through
75μ sieve till the fine dust is fully removed
and the sand was free from all the physical
impurities.
Fill the sand in pycnometer and pour distilled
water till the sand is inundated. Clean the
pycnometer on its outside surface and find its
weight after fully saturation and let the weight
be „A‟.
Empty the pycnometer and fill it with distilled
water only and let the weight be „B‟.
The wet aggregates were cleaned with soft
clothes until the aggregate becomes saturated
surface dried and let the weight be „C‟.
The aggregates were kept in oven and dried it
at a temperature of 100 to 110 degrees
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The aggregates from the oven were removed
and cool to room temperature in the air tight
desiccators and let the weight be „D‟.
Fig 3.4 Pycnometer
FINENESS MODULUS (F.M)
Fineness modulus is an empirical factor obtained by
adding the cumulative percentages retained on each of
the standard sieves and dividing it by arbitrary number
100.
Fineness modulus of sands varies as below
Sand having fineness modulus more than 3.2 will be
unsuitable for making satisfactory concrete
Table 3.3: Shows The Characteristics of Sand
TESTS CONDUCTED FOR CONCRETE MIX
Workability
Workability is the property of concrete which
determines the amount of useful internal work
necessary to produce full compaction. (or) the “ease
with which concrete can be compacted hundred
percent having regard to mode of compaction and
place of deposition.
A concrete mix is said to be workable when it satisfies
the following five properties.
1) Easy to mix
2) Easy to transport
3) Easy to place
4) Easy to compact
5) Easy to finish
The workability is one of the physical parameters of
concrete which affects the strength and durability and
the appearance of the finished surface. The workability
of concrete depends on the water cement ratio and the
water absorption capacity if the aggregates. If the
water added is more which will lead to bleeding or
segregation of aggregates. The test for the workability
of concrete is given by the Indian Standard IS 1199-
1959 which gives the test procedure using various
equipment‟s. In our case we have used slump cone test
and compaction factor test for measuring the
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workability of concrete. We have measured the height
of the fall of the cone of concrete for various water-
cement ratios and recorded the values for ordinary
concrete.
Slump cone test
Compacting factor test
Slump Cone Test
The concrete slump test is an empirical test that
measures the workability of fresh concrete. More
specifically, it measures the consistency of the
concrete in that specific batch. This test is performed
to check the consistency of freshly made concrete.
Consistency is a term very closely related to
workability. It is a term which describes the state of
fresh concrete. It refers to the ease with which the
concrete flows. Workability of concrete is mainly
affected by consistency i.e., wetter mixes will be more
workable than drier mixes, but concrete of the same
consistency may vary in workability. It is also used to
determine consistency between individual batches.
The test is popular due to the simplicity of apparatus
used and simple procedure.
The apparatus for conducting the slump test essentially
consists of metallic mould in the form of a frustum of a
cone having the internal dimensions as under.
Bottom Diameter : 20 cm
Top Diameter : 10 cm
Height : 30 cm
Fig 3.9 Slump Cone Apparatus
Test Procedure
In slump cone the container is filled with concrete in
three layers. Each layer is tamped 25 times with a
standard 16mm diameter steel rod and 600mm height.
The top surface is struck off by means of a screening
and rolling motion of the tamping rod.
Immediately after filling, the cone is slowly lifted and
the unsupported concrete will now slump. The
decrease in the height of the center of the slumped
concrete is called “Slump”. Instead of slumping
evenly all round as in a “True Slump”. One half of the
cone slides down an inclined plane is a “Shear Slump”.
Mixes of stiff consistence have a “Zero Slump”. If any
specimen shears off laterally or collapses, the test
should be repeated.
COMPACTION FACTOR TEST
The compacting factor test is designed primary for use
in the laboratory but it can also be used in the field. It
is more precise and sensitive than the slump test and is
particularly useful for concrete mixes of very low
workability. Such dry concrete are insensitive to
slump test. The diagram of the apparatus is shown in
figure3.10.
The compacting factor test has been developed at the
road research laboratory U. K. And it is claimed that is
one of the most efficient tests for measuring the
workability of concrete. This test works on the
principle of determining the degree of compaction
achieved by a standard amount of work done by
allowing the concrete to fall through a standard height.
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The degree of compaction called the compacting factor
is measured by the density actually achieved in the test
to density of same concrete fully compacted.
Test Procedure
The sample of concrete to be tested is placed
in the upper hopper up to the brim.
The trap-door is opened so that the concrete
falls in to the lower hopper.
Then the trap-door of the lower hopper is
opened and the concrete is allowed to fall in to
the cylinder.
The excess concrete remaining above the top
level of the cylinder is then cut off with the
help of plane scale.
The concrete is filled up exactly up to the top
level of the cylinder.
It is weighed to the nearest 10gms. This
weight is known as “weight of partially
compacted concrete”.
The cylinder is emptied and then refilled with
the concrete from the same sample in layers
approximately 5cm deep.
The layers are heavily rammed or preferably
vibrated so as to obtain full compaction.
The top surface of the fully compacted concrete is then
carefully struck of level with the top of the cylinder
and weighed to nearest 10gms. The weight is known as
“weight of fully compacted concrete”.
It can be realized that compacting factor test measures
the inherent characteristics of the concrete which
relates very close to the workability requirements of
the concrete and as such it is one of the good tests to
depict the workability of concrete.
The compacting factor equipment has been shown
below in fig3.10
Fig 3.10 Compaction Test Apparatus
COMPRESSIVE STRENGTH TEST
Concrete has relatively higher compressive strength,
but very poor in tensile strength. The different mix of
concrete gives various strength, according to the IS
10262: 1982 gives the characteristic and design
strength values for various grades of concrete. The
strength attained by the mix must be tested by its
compressive strength of the samples which are made in
the standard mould of size 150mm X 150mm X
150mm and then the cubes are kept for curing and the
compressive strength test was done according to IS
516: 1959 for 7days, 14days and 28days for ordinary
mix and for the partial replaced samples.
Fig 3.11 Universal Testing Machine
MIX DESIGN (ACI committee 211.1-91 method)
Design of concrete mix needs not only the knowledge
of material properties and properties of concrete in
plastic condition; it also needs wider knowledge and
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experience of concreting. Even then the proportion of
the materials of concrete found out at the laboratory
requires modification and readjustments to suit the
field conditions.
Mix design can be defined as the process of selecting
suitable ingredients of concrete and determining their
relative proportions with the object of producing
concrete of certain minimum strength and durability as
economically as possible. The purpose of designing as
can be seen from the above definitions in two-fold.
The first object is to achieve the stipulated minimum
strength and durability. The second object is to make
the concrete in the most economical manner.
DESIGN STIPULATIONS FOR
PROPORTIONING (Conventional Sand)
Grade designation = M25.
Type of cement = OPC 53 grade.
Maximum nominal size of aggregate = 20 mm.
Maximum water cement ratio = 0.47
Slump = 50mm(Workability).
Degree of supervision = good.
Type of aggregate = crushed angular
aggregate.
Chemical admixtures = not recommended.
Strength of concrete at 28 days = 20N/mm2.
Fineness modulus = 2.8.
Specific gravity of fine and coarse aggregate =
2.65 and 2.7.
Page 172
Results
The following are the results of compressive strengths
of all concrete mixes prepared by replacing CA by
Demolished concrete with various percentages. The
strengths of all concrete mixes are determined a 7, 14,
28 days of curing in water. The following are the
tables showing all the results.
Table 7.1: Variation of Compressive strength with
days of curing for sample 1
Graph 7.1 showing compressive strength at various
days of curing vs % of Demolished concrete
Page 173
Discussion on Compression Value
The compressive strength for the concrete mix
gradually increased with the increase in % of
Demolished concrete added up to 60% of CA replaced
by Demolished concrete and then decreased with
increase in % of Demolished concrete.
As the table and graphs shows the concrete mix
prepared by replacing the 60% of CA by the
Demolished concrete is having the more compressive
strength. If there is a need of concrete with high
compressive strengths in same grade of concrete the
mix with 60% Demolished concrete can be adopted.
But through graphs we cannot judge the exact % at
which the compressive strength is highest. Through the
graph it can be said that the high compressive strength
mix can be get at the percentage between 50 and 70.
But through our experiment we adopt that high
compressive strength mix can be obtained by replacing
60% of coarse aggregate by Demolished concrete.
High compressive strength can be seen in the concretes
with 60% of Demolished concrete replaced in the
place of CA
CONCLUSION
Replacement of natural coarse aggregate by 60%
artificial aggregate gives the maximum compressive
strength.
The concrete mix is more workable when 60% of CA
is replaced by Demolished concrete as the slump
values and compacting factor values are high when
compared to conventional mix.
Finally the concrete mix with 60% of aggregate
replaced by Demolished concrete gives the best mix
with high compressive strength with high workability.
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